MR-9 Battery adapter

MR-9 Battery Adapter

I have previously written about adapting a 675 hearing aid battery for use in cameras that require a 1.35 volt PX625. I was pretty confident at the time that since hearing aid batteries operate at 1.4v that this was the solution to this problem… I have since found out that actually, this solution is not always quite as ideal as I had originally thought.

I recently bought a Leica M3; with it came a Leica MR-4 meter. The Leica MR-4 requires a 1.35v px625 shaped battery. No problem I thought, I will just do my usual trick of padding the battery compartment with playdoh or blutak. Unfortunately, this doesn’t work with the MR-4; it didn’t matter how tight I packed the battery compartment, the connection wasn’t quite positive enough and the meter would stop working in the field. When this happened, I would have to take it off the camera, open the bottom, prod at the blutak a bit… … etc. The photo would be missed.

The solution was initially to try a modern 1.55v PX625. Whilst the battery fit tightly, the voltage was so wrong I would have to adjust the ISO setting to compensate. Normally, this doesn’t bother me, but with a Leica, I just wanted it to be right!

Leica MR-4 with px625
Battery check on the Leica MR-4 – The needle is supposed to be over the white dot – With the PX625 it is quite far out.

A quick search on google and I find the MR-9 battery adapter on Small Battery Company’s website. A website that, by coincidence, had been recommended to me just the day before!

I’ll let you read the technical specs and limitations of this adapter on the Small Battery Company’s website, as they are the experts here. But in short, it allows the use of the very common 386 battery in cameras that require a 1.35v mercury oxide MR9, PX13 or PX625 battery. It does this not only by adapting the shape of the battery, but also by lowering the 1.5v of the 386 to 1.35v.

In the following 3 photos you can see the MR-9 battery adapter on the left, with a modern PX625 on the right.

MR-9 with 386 battery vs px625
Positive side faced up
MR-9 with 386 battery vs px625
Negative side faced up with the MR-9 battery adapter empty
MR-9 with 386 battery vs px625
Negative side faced up with the MR-9 battery adapter with 386 battery slotted in


Here you can see the MR-9 battery adapter fitting perfectly inside the Leica MR-4

Leica MR-4 with MR-9 Adapter in bottom

And finally, the moment of truth… The MR-9 battery adapter giving the Leica MR-4 the correct voltage.

Leica MR-4 with MR-9 Adapter

Works perfectly! The only disadvantage of this solution is the price… At nearly £30 the MR-9 battery adapter is not cheap. Though I suspect this price is due to the economies of small quantity manufacture. And actually, since it is only an adapter, after the initial purchase, it will never run out of power itself, it will just need topping up with the abundant and fairly inexpensive 386 batteries.

Lastly, just a quick thanks to the Small Battery Company who shipped the adapter to me very promptly! I know who I will be buying my camera batteries from in the future!

Cheers for reading!


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10 thoughts on “MR-9 Battery Adapter”

  1. Pingback: The Leica M5 - 35mm

  2. Pingback: Minolta SR-T 202 review - Kosmo Foto

  3. If you apply a volt meter to a 386, properly inserted into a MR-9 adapter, should it read 1.35 volts on the volt meter. Reason I ask, is that I have a 386 that reads 1.58 on my voltmeter – outside the MR-9 and 1.53 in the adapter I was expecting something closer to 1.35 in the adapter

  4. Just purchased my “proper” MR9 adapter from Small Battery Company for my just acquired Yahica MAT-124G. Can’t wait to fit it into the camera!
    Indeed, there are cheap ones on eBay and Amazon that do not seem to have the microelectronics that lower the voltage. Here’s the original description from Small Battery Company (in case it helps anyone go for the proper option and not get fooled by cheap sellers):

    “The “Rolls Royce” solution to problem of the discontinued Mercuric Oxide MR9, PX13 and PX625. Our MR-9 Adapter has the outer dimensions of the PX625 mercury cell with a recess that takes the inexpensive and easily obtained silver oxide 386 cell. Buried within the MR-9 Adapter are micro electronics that drop the voltage from the 1.55 Volts put out by the silver oxide cell to the 1.35 Volts that your camera was designed for.”

  5. Great and thorough article.
    I’ve monkeyed around with old batteries enough in the past to make me avoid any camera that needs the Mercury cell.
    Maybe I’ll give them another chance now I know there is something I can buy to work around the issue.
    Thanks for your commitment to using antique photography equipment!

  6. I recently got burned by those alleged MR9 adapters that DO NOT include the voltage-change resistor. Even worse, the empty little hole where the resister is supposed to go – which should have a bit of wire at the very least – prevents a LR44/SR44 from making contact on that side. Totally useless!

    I got these on Amazon, and while, yes, the description does mention that these “MR9 adapters” don’t change the voltage, it’s buried and very easy to miss. Worse, the package comes without any instructions or documentation. Anyway, if you see the following title on Amazon, AVOID!

    FASTROHY 2Pcs MR-9 Battery Adapter Replacement for Film Camera and Exposure Meter MR9 PX625 PX13

  7. Maybe I just got lucky, but I pretty easily found the correct mercury oxide battery (new old stock) on eBay. It was Varta-branded, still sealed in the original blister pack, and sold by a brick-and-mortar camera store in the US. I’m told it should last for 10 years or more, and it was $15. I’m not opposed to the idea of adapters, but if I have the option of using the original battery (especially at lower cost), I’d rather do that. I only mention this to say that it may be worth a quick search online before deciding that the mercury batteries are unobtanium. I don’t think it’s illegal to buy and sell old mercury batteries, they just can’t be manufactured any more (at least in the US – the EU I think has banned the trade completely, which makes the adapter you’r only legal option I guess).

  8. John H Osterholm

    I ordered two from Amazon and 2 from eBay. The Amazon versions didn’t work in a Canon 7Sz. I assembeled the battery and the adapter and my volt meter read 1.40 Volts but installed in the Canon, it didn’t power up the meter. Any clues?

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